Pharmaceutical compositions

ABSTRACT

Compounds of formula (II) ##STR1## wherein R 1  and R 2  are each separately selected from hydrogen, alkyl, alkenyl and alkynyl groups having up to a maximum of four carbon atoms and being unsubstituted, and alkyl, alkenyl and alkynyl groups having up to a maximum of three carbon atoms and being substituted by one, or in the case of fluoro by one or more, substitutents but with the proviso that when R 1  is hydrogen then R 2  is hydrogen or methyl, or R 1  and R 2  together constitute an ethylene bridging group, and R 3  is a group which under physiological conditions undergoes elimination with the formation of a 3,5-dioxopiperazinyl ring, with the further proviso that the compound is in the meso or erythro configuration when each of R 1  and R 2  is the same or different unsubstituted or substituted alkyl, alkenyl or alkynyl group, and salts thereof with a physiologically acceptable inorganic or organic acid, are of value as prodrugs, particularly in the therapy of cancer and psoriasis.

This invention relates to pharmaceutical compounds and to compositionscontaining them, being primarily concerned with substances of use in thetherapy of cancer including leukaemia, of certain non-malignant forms ofproliferative disease such as psoriasis, and of certain inflammatoryconditions such as uveitis.

In UK Pat. Nos. 1,234,935 and 1,374,979 certain pharmaceuticalcompositions have been described having activity of the above type.These compositions contain as active components compounds of formula (I)wherein R₁ and R₂ are each separately selected ##STR2## from hydrogen,unsubstituted alkyl, alkenyl and alkynyl groups having a chain with upto a maximum of four carbon atoms and substituted alkyl, alkenyl andalkynyl groups having a chain with up to a maximum of three carbon atomsand being limited, except in the case of fluoro, to containing onesubstituent only but with the proviso that when R₁ is hydrogen then R₂is hydrogen or methyl, or R₁ and R₂ together constitute an ethylenebridging group. Although these compounds, particularly that having R₁ =Hand R₂ =CH₃, have proved to be of value in the treatment of both cancerand psoriasis, it is clear that their original promise has not beenfully realised. It has now been found, however, that the administrationof the compounds in a particular prodrug form offers the potential forovercoming the limitations upon their value arising from the use of thecompounds (I) as such.

Accordingly the present invention comprises a compound of formula (II)##STR3## wherein R₁ and R₂ are each separately selected from hydrogen,alkyl, alkenyl and alkynyl groups having up to a maximum of four carbonatoms and being unsubstituted, and alkyl, alkenyl and alkynyl groupshaving up to a maximum of three carbon atoms and being substituted byone, or in the case of fluoro by one or more, substituents but with theproviso that when R₁ is hydrogen then R₂ is hydrogen or methyl, or R₁and R₂ together constitute an ethylene bridging group, and R₃ is a groupwhich under physiological conditions undergoes elimination with theformation of a 3,5-dioxopiperazinyl ring, with the further proviso thatthe compound is in the meso or erythro configuration when each of R₁ andR₂ is the same or different unsubstituted or substituted alkyl, alkenylor alkynyl group, and salts thereof with a physiologically acceptableinorganic or organic acid, for use in therapy.

It has been found that the prodrug compounds (II) do not undergo simplehydrolysis of the two similar ester groups in vivo which would result ina non-cyclic diamide diacid compound of formula (III) as describedhereinafter but instead eliminate two R₃ OH molecules with the formationof the two rings as desired. By modification of the nature of the estergroups it is possible to alter the water solubility, lipophilicity andrate of conversion to the active cytotoxic molecules (I). For examplethe methyl, lower hydroxyalkyl and lower alkoxyalkyl esters have muchgreater water solubilities than the cyclic diimides which they generate,for example the diimide (I) in which R₁ =R₂ =H, has a water solubilityof about 0.01 w/v at 20° C. and pH 7.2 and is therefore difficult to useparenterally whilst also not being well absorbed by mouth, whereas thecorresponding esters in which R₃ =CH₃ or CH₂ CH₂ OH have watersolubilities of >2% w/v and can readily be used for parenteraladministration. Similarly, increased lipophilicity may be obtained inthese prodrugs by the introduction of, for example, hydrocarbongroupings such as isobutyl or benzyl and this is reflected by therelatively high Rf values in a 50% v/v chloroform/ethanol/SiO₂ thinlayer chromatography system as recorded in the Examples givenhereinafter. An increased lipophilicity favours better absorption andchanges in tissue distribution such as greater penetration of thecentral nervous system where leukaemic cells can otherwise obtainsanctuary. The more lipophilic products are also the most attractivecandidates for the percutaneous treatment of psoriasis. Further,depending upon whether R₃ is an electron-withdrawing group, for examplebenzyl, propargyl or carbethoxymethyl, or an electron-repelling group,for example isobutyl, hydroxyethyl or methoxyethyl, the rate ofconversion of the compound (II) to the corresponding compound (I) can bespeeded up or slowed down. Thus, by providing some control over thewater solubility, lipophilicity and rate of generation of the activespecies, the prodrug compounds of the present invention provide theability to modify the tissue distribution and pharmacodynamics of thedioxopiperazine antitumour drugs with consequential therapeutic benefitto the patient.

The group R₃ is eliminated under physiological conditions and, althoughit is possible that enzymic catalysis may be involved in some cases, theelimination will usually occur spontaneously and may be tested for invitro by incubation of the compound (II) under physiological conditions(i.e. pH 7.2, 37° C.), for example as described in Example 11(B). Whilsta very wide range of alkyl, alkenyl and alkynyl groups having a maximumof up to ten carbon atoms and being unsubstituted or substituted may beused as the group R₃, it has been found that certain groups R₃ such ast-butyl groups normally undergo S_(N) 1 reactions which do not involvecyclisation so that no significant amount of the desired compound (I) isproduced. For this reason, the unsubstituted and substituted alkyl,alkenyl and alkynyl groups R₃ of use in the present invention preferablycontains a bonding carbon atom, i.e. that atom linked to the group##STR4## which carries at least one hydrogen atom. Subject to thispreference, R₃ may conveniently be selected from alkyl, alkenyl andalkynyl groups having up to a maximum of ten carbon atoms which may beeither unsubstituted or substituted. Preferred groups R₃ are suchunsubstituted alkyl, alkenyl and alkynyl groups and aralkyl, aralkenyland aralkynyl groups in which the aromatic part of the group mayoptionally be substituted by one or two substituents selected fromhalogen, lower alkyl, lower alkoxy (including a single methylenedioxy),amino and nitro groups and the aliphatic part of the group, which is ofa similar size to the unsubstituted aliphatic groups, may optionally besubstituted by one substituent selected from alkoxycarbonyl and cyano.Another preferred form for R₃ is alkyl, alkenyl and alkynyl groups whichhave a maximum of up to ten carbon atoms and which are substituted byone or more halogeno (for example fluoro, chloro or bromo), hydroxy,alkoxycarbonyl, benzyloxycarbonyl, cyano, amino (and mono anddialkylamino) groups, or alternatively alkoxy or carboxy groups. Amongthese, the substituted alkyl groups, especially the alkoxyalkyl groupswhich may conveniently contain up to a maximum of ten carbon atoms intotal, are of particular interest. Another form of substituted alkyl,alkenyl and alkynyl group which is preferred is that containing an oxosubstituent, for example the oxo-alkyl groups acetonyl and phenacyl,such groups providing ketonic esters, particularly β-keto esters.

Among the various alkyl, alkenyl and alkynyl groups R₃, bothunsubstituted and substituted, it is preferred for reasons of ease ofsynthesis and stability of the compound (II) prior to administrationthat the bonding carbon atom of the group, as defined hereinbefore, isnot linked to any atom which is not hydrogen or carbon and, moreover,conveniently also is not unsaturated, i.e. is not linked to any adjacentatom by a double or particularly a triple bond. Moreover, while thegroups, for example alkyl groups, may be substituted by one or moresubstituents, groups containing one or two substituents are preferred,and conveniently only one substituent in most cases although with somesubstituent groups, such as alkoxycarbonyl groups, the presence of twosubstituents may be of value. Those comments also apply to aralkyl,aralkenyl and aralkynyl groups which most usually contain two orparticularly one aryl group, although groups such as the diphenylmethylgroup may be of interest in resisting the esterase activity which occursin some animal species as discussed hereinafter. As regards the aromaticgroups, the preferred form of group is an unsubstituted or substitutednaphthyl or particularly phenyl group.

It should be appreciated that the terms alkyl, alkenyl and alkynyl areused throughout this specification to include both straight and branchedgroups. Alkyl, alkenyl and alkynyl groups R₃ of one to four carbon atomsin the case of alkyl groups and two to four carbon atoms in the case ofalkenyl and alkynyl groups are of most interest, whether unsubstitutedor substituted. The terms lower alkyl and lower alkoxy are used in thediscussion of the substituent groups in R₃ to indicate a group of one tofour carbon atoms and in those cases where the term alkyl or alkoxy isused without qualification the preference is for groups of one to tencarbon atoms, particularly of one to four carbon atoms.

Preferred groups R₃ are unsubstituted alkyl, alkenyl and alkynyl groupsand substituted alkyl groups (including aralkyl groups). Specificexamples of preferred groups R₃ are as follows (the terms ethyl, propyland butyl used without qualification in the names of the substitutedgroups as usual indicate a substituted n-alkyl group (and similarly foralkoxy groups present as a substituent) but, except where indicated,without any restriction upon the position of the substituent in thecarbon chain of that alkyl group although, as mentioned hereinbefore,substitution upon the bonding carbon atom is generally of lesserinterest, substitution upon the terminal carbon of the chain usuallybeing of most interest; in the cases where R₃ is a substituted benzylgroup, substitution at the α-position is specifically indicated andwhere this is not done the substituent is located on the ring): methyl,ethyl, n-propyl, n-butyl, isobutyl, allyl, propargyl, benzyl,α-methylbenzyl, α-ethoxycarbonylbenzyl (i.e. α-carbethoxybenzyl),nitrobenzyl, aminobenzyl, mono and dichlorobenzyl,chloro-3,4-methylenedioxybenzyl (i.e. chloropiperonyl), mono anddimethoxybenzyl, mono and dimethylbenzyl, cinnamyl, methoxyethyl,ethoxyethyl, propoxyethyl, butoxyethyl, hydroxyethyl, hydroxypropyl,hydroxybutyl, ethoxycarbonyl methyl (i.e. carbethoxymethyl),ethoxycarbonylethyl, ethoxycarbonylpropyl, carboxymethyl, carboxyethyl,carboxypropyl, benzyloxycarbonylmethyl, benzyloxycarbonylethyl,benzyloxycarbonylpropyl, t-butoxycarbonylmethyl, t-butoxycarbonylethyl,t-butoxycarbonylpropyl, diethoxycarbonylmethyl, cyanomethyl, acetonyl,phenacyl, and 3-dimethylaminopropyl, the alkyl groups preferably beingterminally substituted where more than one possibility exists. Specificgroups R₃ are further illustrated by those present in the compounds ofthe Examples.

Preferably the carbon chain of the groups R₁ and R₂, which may bestraight or branched, contains from one to three carbon atoms in thecase of alkyl groups and two to three carbon atoms in the case ofalkenyl and alkynyl groups. More conveniently, when the groups aresubstituted, particularly by substituent groups other than fluoro, theycontain one or two carbon atoms in the case of alkyl groups and twocarbon atoms in the case of alkenyl and alkynyl groups. Althoughsubstituted groups R₁ and R₂ are in general of rather lesser interest,some substituted alkyl, and also alkenyl and alkynyl groups, do howeverpossess certain advantages, for example enhanced solubility of theactive compound (I), but this is of lesser importance when a prodrugform of the compound is administered. The various substituents which maybe present include phenyl, carboxy and alkoxycarbonyl (i.e. carbalkoxy)groups but more particularly halogeno, hydroxy and alkoxy groups. It ispreferred that the size of the groups R₁ and R₂ is not too great sincethis tends to lead to a reduction in activity, and for this reasoncompounds in which the substituent group is located at the terminalcarbon atom of the chain are preferred. In general those compounds inwhich both R₁ and R₂ are relatively large substituted groups are of lessinterest, those in which only one of R₁ and R₂ is substituted being ofmore interest. Conveniently the substituted groups are limited to thosehaving a steric effect in the molecule not substantially greater thanthat of an isopropyl group. Thus, preferred substituents are fluoro,hydroxy and methoxy, but also chloro and additionally ethoxy, carboxyand methoxycarbonyl. For similar reasons it is preferred that the numberof fluoro atoms in any substituted group is limited to five andconveniently to three. Moreover, particularly in the case ofsubstituents such as phenyl, ethoxy, carboxy and methoxycarbonyl, butalso with other substituents, substituted ethyl, and particularlysubstituted methyl groups are of especial interest.

Examples of specific substituted groups R₁ and R₂ are the substitutedsaturated groups chloromethyl, pentafluoroethyl, and particularlyhydroxymethyl, 2-hydroxyethyl, methoxymethyl, trifluoromethyl and2,2,2-trifluoroethyl. However, as indicated hereinbefore, theunsubstituted groups R₁ and R₂ are of greater interest, preferredcompounds (II) being those in which both R₁ and R₂ are hydrogen, or R₁is methyl and R₂ is hydrogen, methyl, ethyl, n-propyl, isopropyl, allylor propargyl, or R₁ and R₂, which are different or preferably the same,are both selected from ethyl, n-propyl, isopropyl, allyl and propargyl,or R₁ and R₂ together represent an ethylene bridging group.

Particularly preferred are those compounds where both R₁ and R₂ arehydrogen or R₁ is methyl and R₂ is methyl, ethyl or especially hydrogen,or both R₁ and R₂ are ethyl, whilst R₃ is selected from methyl, ethyl,isobutyl, allyl, propargyl, benzyl, α-methylbenzyl, α-carbethoxybenzyl,o-nitrobenzyl, aminobenzyl, 2,6-dichlorobenzyl, methoxyethyl,ethoxyethyl, propoxyethyl, butoxyethyl, hydroxyethyl, hydroxypropyl,hydroxybutyl, ethoxycarbonylmethyl, diethoxycarbonylmethyl,benzyloxycarbonylmethyl, ethoxycarbonylpropyl, carboxymethyl andacetonyl.

As indicated hereinbefore, when neither R₁ nor R₂ is hydrogen, thecompounds (II), like the compounds (I), are limited to those in whichthe groups R₁ and R₂ are adjacently disposed in the meso or erythroconfiguration rather than oppositely disposed in the dl or threo,configuration except that in the particular case when R₁ and R₂ togetherconstitute an ethylene bridging group the configuration of the resultantcyclobutane ring may be cis or trans. However, when R₁ and R₂ are notidentical the compounds can exist in two enantiomorphic forms, theinvention including the use of the various different isomers of suchcompounds. In some cases the optically active d- and l-isomers may havethe advantage of significantly higher water solubility than thecorresponding dl-racemate and it may also be the case that thebiological activity of the compound will differ as between the isomers.The invention does therefore extend to the use of such compounds in aform in which the amount of the compound in the d or l configuration isgreater than that in the l or d configuration. In particular thecompound may be essentially in the form of the d or l isomer, forexample being substantially free (i.e. containing no more than 10%) fromthe dl and l or dl and d isomers.

The preparation of the simplest compound (II) of use in the presentinvention (R₁ =R₂ =H and R₃ =CH₃) has been described by Houghton andWilliams (Journal of the Chemical Society, Perkin Transactions I, 1982,2693) in a paper relating to chemical synthesis, there having been nosuggestion that the compound might possess any pharmaceuticalproperties. The remaining compounds (II) are novel, per se.

Accordingly, the present invention further comprises a compound offormula (II) ##STR5## wherein R₁ and R₂ are each separately selectedfrom hydrogen, alkyl, alkenyl and alkynyl groups having up to a maximumof four carbon atoms and being unsubstituted, and alkyl, alkenyl andalkynyl groups having up to a maximum of three carbon atoms and beingsubstituted by one, or in the case of fluoro by one or more,substituents but with the proviso that when R₁ is hydrogen then R₂ ishydrogen or methyl, or R₁ and R₂ together constitute an ethylenebridging group, and R₃ is a group which under physiological conditionsundergoes elimination with the formation of a 3,5-dioxopiperazinyl ring,with the further proviso that when each of R₁ and R₂ is hydrogen then R₃is not methyl and that the compound is in the meso or erythroconfiguration when each of R₁ and R₂ is the same or differentunsubstituted or substituted alkyl, alkenyl or alkynyl group, and saltsthereof with a physiologically acceptable inorganic or organic acid.

In the single literature report of the preparation of a compound (II)(R₁ =R₂ =H and R₃ =CH₃) the copper chelate of the bis cyclic imide (I,R₁ =R₂ =H) is reacted with an excess of methanol and the copper issubsequently removed from the product with hydrogen sulphide. Thismethod works well with methanol but is less successful with ethanol (togive II, R₁ =R₂ =H and R₃ =C₂ H₅) and becomes progressively moredifficult with higher alcohols. We have found that it is advantageous toreplace the cupric chloride used by Houghton and Williams to make theinitial chelate by a cupric salt of a sulphonic acid such as methanesulphonic or isethionic acid. These give more soluble intermediateswhich lead to more efficient reactions and, after treatment withhydrogen sulphide, to the direct isolation of more water soluble,pharmaceutically acceptable salt forms of the described products. It maysometimes also be advantageous to add about two equivalents of freesulphonic acid, for example methane sulphonic acid, to the initialreaction mixture. Reasonable yields of diesters from higher alcoholssuch as 2-butoxyethanol may also be obtained by using an ester exchangereaction between the dimethyl ester, activated in the form of the copperchelate and an excess of the appropriate alcohol. Treatment withhydrogen sulphide may again be used to liberate the desired product. Theuse of other forms of activated ester for this purpose may also beemployed.

A more generally useful method, particularly appropriate where thealcohol is not a liquid, or is uneconomic to use in excess or ispH-labile, is neutral esterification using caesium salts and theappropriate, more reactive, halide as described for simple N-acyl aminoacids by Wang et al, (Journal of Organic Chemistry, 1977, 42, 1286). Inthis procedure the appropriate diacid diamide (prepared as described byHuang et al, Agents and Actions, 1982, 12, 536) is carefully neutralisedwith caesium bicarbonate (or caesium carbonate) and a solution, or moreusually a suspension, of the dried salt in a neutral aprotic solventsuch as dimethylformamide, is treated with a reactive halide such asbenzyl bromide. The reaction is usually complete within a few hours atfrom 50° to 100° C. Alternative solvents include hexamethylenephosphoramide, dimethylsulphoxide and N-methylpyrrolidone and thecaesium salts can generally be replaced by rubidium salts and, infavourable cases where the halide is particularly reactive such as withthe benzyl halides, by salts of other metals including sodium orpotassium as well as by salts of tertiary amines such as triethylamineor 4-dimethylaminopyridine.

Yet another procedure involves the use of an acetal of dimethylformamideof formula (R₃ O)₂ CH.N(CH₃)₂ which is reacted with the appropriatediacid diamide, conveniently by heating the two reactants in a suitablemutual solvent, an excess of the acetal generally being employed.Reaction at 50° to 100° C. is usually appropriate, refluxing benzenebeing suitable as the reaction medium in many cases. This reaction isparticularly adapted to the preparation of compounds in which R₃ is anunsubstituted alkenyl, alkynyl or particularly alkyl group, for exampleethyl, methyl, isopropyl, n-propyl, n-butyl etc.

It will be appreciated that the present invention includes a process forthe preparation of a compound of formula (II). ##STR6## wherein R₁ andR₂ are each separately selected from hydrogen, alkyl, alkenyl andalkynyl groups having up to a maximum of four carbon atoms and beingunsubstituted, and alkyl, alkenyl and alkynyl groups having up to amaximum of three carbon atoms and being substituted by one, or in thecase of fluoro by one or more, substituents but with the proviso thatwhen R₁ is hydrogen then R₂ is hydrogen or methyl, or R₁ and R₂ togetherconstitute an ethylene bridging group, and R₃ is a group which underphysiological conditions undergoes elimination with the formation of a3,5-dioxopiperazinyl ring, with the further proviso that when each of R₁and R₂ is hydrogen then R₃ is not methyl and that the compound is in themeso or erythro configuration when each of R₁ and R₂ is the same ordifferent unsubstituted or substituted alkyl, alkenyl or alkynyl group,and salts thereof with a physiologically acceptable inorganic or organicacid, which comprises reacting a compound of formula (III) ##STR7## or arelated compound in which the carboxy groups are in derivature form,including that form in which the carboxyl groups are derivatised by theamide groups to form 3,5-dioxopiperazinyl rings, with an alcohol R₃ OHor a derivative thereof, where appropriate using a compound of formula(III) or a related compound in the form of a salt with a physiologicallyacceptable inorganic or organic acid or reacting the compound (II) fromthe reaction with the alcohol R₃ OH or derivative thereof with such anacid to form a salt.

As discussed hereinbefore, the alcohol R₃ OH is preferably a primary orsecondary one, i.e. the carbon atom joined to the hydroxy group carriesone or two hydrogen atoms, in order to produce a compound (II) in whichthe bonding carbon atom of the group R₃ carries at least one hydrogenatom, which would not be the case with a tertiary alcohol. To obtaincompounds (II) of the desired stereochemistry it is most convenient touse a compound (III) or a related compound having the equivalentstereochemistry. When a d or l isomer is required rather than the dlisomer, however, an alternative to the utilisation of a d or l compound(III), which is preferred, is to effect a resolution of the compound(II), for example using an appropriate optically active acid to form amixture of salts of the d and l forms of the compound (II) which arethen separated.

The present invention also includes pharmaceutical compositionscomprising as an active component a compound of formula (II) as definedhereinbefore, together with a physiologically acceptable diluent orcarrier. As indicated, the compounds may be formulated as salts withphysiologically acceptable inorganic or organic acids and, when soformulated, it is preferred to use methane sulphonic acid, isethionicacid, tartaric acid or another solubilising acid.

The compunds of formula (II) may be formulated for use aspharmaceuticals by a variety of methods. For instance, they may beapplied as aqueous, oily (e.g. as a suspension in isopropyl myristate),or in some cases emulsified compositions for parenteral administrationand therefore preferably sterile and pyrogen-free. Some of thesecompounds have rather low solubility in aqueous media and are thereforeusually administered in the form of aqueous suspensions containingsuitable surface active agents. It will be appreciated that the dosagelevels used may vary over quite a wide range especially since certain ofthe compounds (I) are more active than others and as the rate offormation of these compounds will depend upon the particular nature ofthe group R₃ in the compound (II) which is being used. Withoutcommitment to a rigid definition of dosages it may be stated that adaily dosage of active constituent (estimated as the free base), dividedif necessary, of from 10 mg to 3 g is proposed for mammalian use appliedas a solution in 500-1000 ml of liquid for intravenous injection by slowinfusion, or as a solution or suspension in about 10 ml of liquid by theintramuscular route, or in small volumes subcutaneously. Moreparticularly, by way of example, when the active compound (II) has agroup R₁ which is hydrogen or methyl and a group R₂ which is hydrogenthe daily dose for a 70 kg human, administered parenterally will oftenbe in the range from 100 mg to 500 mg but with the more active compoundsin which R₁ is methyl and R₂ is methyl or ethyl it will tend to be lessthan this (the dose being varied pro rata for humans of a differntweight or other mammals).

The substances may also be compounded for oral administration in dosageswhich may be similar but may often be somewhat higher, for example in arange from 100 mg to 1 g or even as high as 3 g for the daily dose for a70 kg human when R₁ =H or CH₃ and R₂ =H but often somewhat less thanthis when R=CH₃ and R₂ =CH₃ or C₂ H₅. Such oral formulations mayparticularly take the form of tablets compounded in the presence ofconventional solid carrier materials such as starch, lactose, dextrinand magnesium stearate, or of capsules, aerosols or cachets. For thetreatment of local forms of the disease, compositions adapted fortopical application may be used, for example suitable creams or dropsmay be prepared containing the active substance or an aerosolformulation. Suppositories, pessaries and other formulations may also beemployed. The compounds may be formulated in unit dosage form, i.e. indiscrete portions each containing a unit does, or a multiple orsub-multiple of a unit dose of the active ingredient.

It will be appreciated that certain formulations of the compounds (II)will tend to cyclise to the compounds (I) on storage if made up inadvance. For this reason, although the compounds may conveniently beformulated in advance of their use as a solid composition it willusually be appropriate to prepare certain forms of liquid composition,particularly those containing an aqueous diluent, just prior to theiruse. Providing such steps are taken to avoid premature cyclisationbefore administration, however, it will be appreciated from theforegoing discussion that the compounds used may have a very wide rangeof half lives in vivo.

The compounds are of value in the treatment of a variety of forms ofcancer, for example sarcomas (including lymphosarcomas), carcinomas(particularly colorectal carcinomas), and leukaemias. In addition theyare of value in the treatment of psoriasis and of certain forms ofinflammatory activity, particularly inflammatory conditions of the eyesuch as uveitis, but also inflammatory bowel disease. They areapplicable primarily in the treatment of humans and although they canfind veterinary use in certain other mammals such as dogs, rabbits,cattle, and horses, their activity is not expressed in rodents such asrats and mice owing to an esterase activity existing in the plasmathereof which prevents cyclisation of the compounds (II) to thecompounds (I).

If desired, a mixture of two or more compounds (II) may be employed inthe present invention. Moreover, it is also possible to use thecompounds (II) in combination with other compounds of value in thetreatment of cancer and proliferative diseases and also in conjunctionwith radiation, a synergistic effect being observed in some cases. Inparticular, they can be combined advantageously with anthracycline drugssuch as doxorubicin and provide a protective effect against thecardiotoxicity of these agents.

The invention is illustrated by the following Examples.

EXAMPLE 1

A mixture of 1,2-bis-(3,5-dioxopiperazin-1-yl)ethane (25.4 g, 0.1 moles)(prepared as described in UK patent specification No. 1,234,935), cupricmethanesulphonate (25.4 g, 0.1 moles) (prepared from equivalent amountsof cupric acetate ad methanesulphonic acid) and dry methanol (500 ml)was stirred and heated together under reflux for 48 hours. The reactionmixture was then evaporated to dryness and the residue taken up in water(200 ml), saturated with hydrogen sulphide and then filtered. Thecolourless solution was evaporated to dryness to yield a white solidwhich was recrystallised from methanol (100 ml) containing a littlewater to give, on cooling, 25.5 g of the methyl diester. Concentrationof the mother liquors to 50 ml followed by dilution with acetone (50 ml)gave on cooling a further 7.0 g yielding a total of 32.5 g (62%) ofNN'-Dimethoxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethanedimethanesulphonate monohydrate. Both crops had m.p. 189°-190° (dec).Treatment of a sample suspended in chloroform with dry ammonia gave thebase, m.p. 140°-142° C. from methanol.

Similarly prepared from the appropriate alcohols and bis-imides were:

dl-NN'-Dimethoxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropane,as the free base in 15% yield (after conversion from thedimethanesulphonate), m.p. 107°-108° from n-propanol/cyclohexane.

NN'-Diethoxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethanedimethanesulphonate monohydrate, (60% yield) m.p. 186°-187° (dec) fromaqueous ethanol. The free base has m.p. 138°-139° from ethanol.

NN'-Di-isobutoxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethanedimethanesulphonate (42% yield), m.p. 187° C. (dec) from aqueousacetone.

NN'-Di-(2-methoxyethoxy)carbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,as the free base in 36% yield (after conversion from thedimethanesulphonate), m.p. 120°-123° from ethanol.

NN'-Di-isopropoxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,as the free base in 37% yield, m.p. 188°-189° C. from ethanol. (Twoequivalents of p-toluensulphonic acid were added to help increase thesolubility of the reactants and consequently the product initiallyisolated was a mixture of methanesulphonate and toluenesulphonatesalts).

NN'-Di-(2-hydroxyethoxy)carbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethanedimethanesulphonate monohydrate, (16% yield), m.p. 175°-176° C. (dec)from isopropanol.

NN'-Di-(2-n-butoxyethoxy)carbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,as the free base in 4% yield, m.p. 99°-100° C. (dec) from isopropanol.

EXAMPLE 2

An aqueous solution of caesium carbonate (16 ml, 20%, 10 mmoles) wasadded dropwise to a stirred suspension ofdl-NN'-dicarboxymethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropanemonohydrate (prepared as described by Huang et al, Agents and Actions,1982, 12, 536) (3.22 g, 10 mmoles) in methanol (40 ml) and water (10 ml)at below -5° C. The clear solution was then evaporated to dryness at orbelow 20° C. The dried solid residue was suspended in dimethyl formamide(80 ml) and stirred overnight at room temperature with propargyl bromide(1.7 ml, 22 mmoles). The temperature was raised over half an hour up to80° C. and the caked solid broken up as far as possible with a spatula.Heating was continued for 11/2 hours and the reaction mixture thenevaporated to dryness and partitioned between water and methylenechloride. Concentration of the methylene chloride layer gave an oilwhich crystallised from isopropanol to give 2.1 g of the crude propargyldiester. Recrystallisation from isopropanol containing a very littlemethanol gave

dl-NN'-Dipropargyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropane,1.76 g (46%), m.p. 99°-101° C.

Similarly prepared from the appropriate halides and bis acid/amideswere:

dl-NN'-Dibenzyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropane,prepared from benzyl bromide in 34% yield, m.p. 92°-93° C. frommethanol/isopropanol.

dl-NN'-Di-p-nitrobenzyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropane,prepared from p-nitrobenzylbromide in 53% yield, m.p. 153°-154° C. frommethanol.

EXAMPLE 3

A suspension of CsHCO₃ (1.94 g, 10 mmoles) in methanol (25 ml) was addedslowly to a stirred suspension ofdl-NN'-dicarboxymethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropanemonohydrate (1.61 g, 5 mmoles) in methanol at -20° C. and the mixtureallowed to warm up to 10° C. during an hour when complete solution wasachieved. The solution was evaporated to dryness and the residuesuspended in dimethylformamide (50 ml) and treated with phenacyl bromide(2.19 g, 11 mmoles). The reaction mixture was heated with stirring up to70° C. over a hour, at 70° C. for 2 hours and then at 100° C. for 2hours and then evaporated to dryness. The residue was triturated withchloroform, filtered from caesium bromide (1.8 g) and the filtrateevaporated to an oil which crystallised from ispropanol to give, afterrecrystallation, 1.54 g (54%) ofdl-NN'-Diphenacyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropane,as a dihydrate, m.p. 80°-81° C.

Similarly prepared from the appropriate halides and bis acid/amideswere:

dl-NN'-Di-(2,6-dichlorobenzyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminopropane,prepared from 2,6-dichlorobenzyl bromide in 69% yield, m.p. 157°-158° C.from dimethylformamide/methanol.

dl-NN'-Di-o-nitrobenzyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminopropane,prepared from o-nitrobenzyl bromide in 44% yield, m.p. 135°-136° C. frommethanol.

EXAMPLE 4

The following compounds were prepared according to the general procedureof Example 2 except that an equivalent amount of caesium bicarbonaterather than caesium carbonate was used to prepare the initial caesiumsalts:

NN'-Dibenzyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from benzyl bromide in 27% yield, m.p. 169°-170° C.

NN'-Diphenacyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from phenacyl bromide in 83% yield, m.p. 200°-203° C. frommethanol.

NN'-Di-p-nitrobenzyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from p-nitrobenzyl bromide in 64% yield, m.p. 195°-196° C. fromdimethylformamide.

NN'-Di-(2,6-dichlorobenzyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from 2,6-dichlorobenzyl bromide in 80% yield, m.p. 202°-203° C.from dimethylformamide/methanol.

NN'-Di-(6-chloropiperonyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from 6-chloropiperonyl bromide in 14% yield, m.p. 165°-168° C.from dimethylformamide.

NN'-Di-(ethoxycarbonylmethyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from ethyl chloroacetate in 78% yield, m.p. 142°-143° C. frommethanol.

NN'-Di-(3-ethoxycarbonylpropyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from ethyl-4-bromobutyrate in 37% yield m.p. 195° C. fromdimethylformamide.

NN'-Di-(benzyloxycarbonylmethyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from benzyl bromoacetate in 57% yield, m.p. 127°-128° C. frommethanol.

NN'-Di-(t-butoxycarbonylmethyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from t-butyl bromoacetate in 29% yield, m.p. 105°-107° C. frommethanol/isopropanol.

NN'-Di-(1-phenyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from α-methylbenzyl bromide in 6% yield, m.p. 138°-141° C. frommethanol.

NN'-Di(diethoxycarbonylmethyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from diethyl α-bromomalonate in 8% yield, m.p. 78°-79° C. fromethanol.

meso-NN'-Di-(benzyloxycarbonylmethoxyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-2,3-diaminobutane,prepared from benzyl bromoacetate in 67% yield, m.p. 152°-153° C. frommethanol.

NN'-Di-(propargyloxycarbonylmethyl)-NN'-diaminocarbonymethyl-1,2-diaminoethane,prepared from propargyl bromide in 31% yield, m.p. 127°-128° C. fromisopropanol.

NN'-Di-(cyanomethylcarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,prepared from chloroacetonitrile in 10% yield.

EXAMPLE 5

NN'-Di-(benzyloxycarbonylmethyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diaminoethane(7.0 g, 11.9 mmoles) in dimethylformamide (200 ml) was hydrogenated overa palladium/charcoal catalyst (0.7 g) at about 40° C. to maintainsolution. After 1/2 hour the reaction appeared complete (TLC) and thecatalyst was removed by filtration. Concentration and crystallisationgaveNN'-Di-(carboxymethyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-1,2-diamonoethane,4.5 g (93%), m.p. 180°-181° C. from dimethyl formamide/ethanol.

Similarly prepared from the corresponding dibenzyl ester was:meso-NN'-Di-(carboxymethyloxycarbonylmethyl)-NN'-diaminocarbonylmethyl-2,3-diaminobutane,in near quantitative yield, m.p. 210°-211° C. fromdimethylformamide/ethanol/acetone.

EXAMPLE 6

NN-Dimethylformamide diethylacetal (16.2 g, 80 mmoles; Pierce ChemicalCompany) was added dropwise during 10 minutes to a stirred suspension ofNN'-dicarboxymethyl-NN'-diaminocarbonylmethyl- b 1,2-diaminoethane (2.9g, 10 mmoles) in dimethylformamide (75 ml) at 100° C. After a further 30minutes at 100° C., the solvent was evaporated off under reducedpressure and the residue crystallised from isopropanol. Furtherrecrystallisation from ethanol gaveNN'-diethoxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,m.p. 130°-140° C.

EXAMPLE 7

A mixture of 1,2-bis(3,5-dioxopiperazin-1-yl)ethane (25.4 g, 0.1 moles)and cupric methane sulphate (25.4 g, 0.1 moles) in dry methanol (500 ml)was heated under reflux for 48 hours. The methanol was removed byevaparation under reduced pressure and replaced by 2-n-butoxyethanol(500 ml) and the resultant solution heated under nitrogen for 10 hoursat 120° C. The solvent was removed by evaporation under reduced pressureand the residue taken up in warm acetic acid (300 ml) and water (100ml). The solution was then saturated with H₂ S, filtered throughKeiselguhr and the filtrate evaporated to a low bulk. The residue wasdissolved in water (100 ml), and crushed ice (100 g) and an excess ofsodium acetate were added and the mixture extracted several times withchloroform. The microcrystalline material obtained on evaporation waspurified by passing 0.5 g batches through a Zorbax ODS HPLC column (2.5cm×28 cm) using gradient elution with methanol/water and a 3 mlinjection loop. The product was crystallised from isopropanol to giveNN'-Di-(2-n-butoxyethoxy)carbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminoethane,14.6 g (32%), m.p. 99°-100° C. (dec).

EXAMPLE 8

Tablets of the following composition are prepared:

    ______________________________________                                                            mg/tablet                                                 ______________________________________                                        Compound of Example 2 (micronised)                                                                  250                                                     `Avicel` (microcrystalline cellulose)                                                               38                                                      polyvinylpyrrolidone  3                                                       alginic acid          6                                                       magnesium sterate     3                                                       ______________________________________                                    

Any one of the products prepared in Example 2 is mixed with `Avicel` andpolyvinylpyrrolidone is added, dissolved in sufficient industrialmethylated spirits (74° OP) to produce a mass suitable for granulating.The mass is granulated through a 20 mesh sieve and the resultantgranules are dried at a temperature not exceeding 50° C. The driedgranules are passed through a 20 mesh sieve and the alginic acid andmagnesium sterate are then added and mixed with the granules. Theproduct is compressed into tablets each weighing 300 mg on 3/8 inch flatbevelled edge divided punches.

EXAMPLE 9

Tablets of the following composition are prepared:

    ______________________________________                                                            mg/tablet                                                 ______________________________________                                        Compound of Example 2 (micronised)                                                                  250                                                     `Avicel` (microcrystalline cellulose)                                                               134                                                     polyvinylpyrrolidone  4                                                       alginic acid          8                                                       magnesium sterate     4                                                       ______________________________________                                    

The tablest are prepared by essentially the same procedure as describedin Example 6, using any one of the products prepared in Example 2, andare compressed at a tablet weight of 400 mg on 7/16 inch flat bevellededge punches.

EXAMPLE 10

Tablets of the following composition are prepared:

    ______________________________________                                                            mg/tablet                                                 ______________________________________                                        Compound of Example 2 (micronised)                                                                  250                                                     lactose (300 mesh)    19                                                      maize starch          15                                                      gelatine              10                                                      magnesium sterate      6                                                      ______________________________________                                    

The tablets are prepared by mixing any one of the products prepared inExample 2 with lactose and half the total quantity of maize startchrequired, and adding to the mass a 5% solution of gelatine in water. Theproduct is granulated through a 16 mesh sieve, and the resultantgranules are dried to constant weight at a temperature not exceeding 50°C. The dried granules are passed through a 20 mesh sieve and mixed withmagnesium stearate and the remainder of the maize starch. The product iscompressed at a 300 mg tablet weight on 3/8 inch flat bevelled edgedivided punches.

EXAMPLE 11

(A) The cytotoxic effects of a variety of compounds of formula (II) onhuman adenocarcinoma cells of the colon (LOVO) and human mammaryepithelial tumour cells (MCF7) grown in culture were studied. A range ofdoses of the drugs was added on day one to replicate cultures of severalhundred cells each, which were then incubated at 37° C. for 12-14 days.The cultures were then fixed and stained and the numbers of colonies perdish counted. The results obtained are shown in Table 1, the individualcompounds being identified by the groups R₁, R₂ and R₃ present therein,the last mentioned compound being the compound of formula (I) having R₁=H and R₂ =CH₃ which is used as a control. The results are expressed interms of the ID₅₀ which is the dose required to reduce by 50% the numberof colonies growing up in the drug-treated cultures compared withuntreated controls.

                  TABLE 1                                                         ______________________________________                                        Compound               ID.sub.50 (μM)                                      R.sub.1                                                                              R.sub.2 R.sub.3         LOVO  MCF7                                     ______________________________________                                        H      H       CH.sub.3        28    39                                       H      H       CH.sub.2 CH(CH.sub.3).sub.2                                                                   103   121                                      CH.sub.3                                                                             H       CH.sub.2 C.sub.6 H.sub.5                                                                      17    22                                       H      H       CH.sub.2 CH.sub.2 O(CH.sub.2).sub.3 CH.sub.3                                                  47    36                                       CH.sub.3                                                                             H       p-NO.sub.2 --CH.sub.2 C.sub.6 H.sub.5                                                         14    21                                       H      H       CH.sub.2 CO.sub.2 H                                                                           67    46                                       CH.sub.3                                                                             H       o-NO.sub.2 --CH.sub.2 C.sub.6 H.sub.5                                                         11    16                                       CH.sub.3                                                                             CH.sub.3                                                                              CH.sub.2 CO.sub.2 H                                                                           0.2   1.1                                      H      H       CH(CH.sub.3)C.sub.6 H.sub.5                                                                   35    31                                       H      H       CH(CO.sub.2 C.sub.2 H.sub.5).sub.2                                                            18    25                                       CH.sub.3                                                                             H       cyclic imide    18    17                                       ______________________________________                                    

(B) The rate of formation of the active antitumour agent (I) having R₁ =and R₂ =H from the corresponding ¹⁴ C-labelled dimethyl ester (II) (R₁=R₂ =H, R₃ =CH₃) following incubation under physiologically conditions,i.e. at 37° C. and pH 7.2 in normal (0.15M) phosphate buffered saline[Practical Immunology, Hudson and Hay (editors), Blackwell ScientificPublications, Second Edition, 1980, page 336] was studied. Samples ofthe incubation mixture were fractionated at different time intervalsusing HPLC with a reverse phase ODS column and an aqueous methanolgradient elution system. The results are shown in the FIGURE from whichit will be seen that although the diimide itself hydrolyses to aninactive form, having a half life of about 12 hours at pH 7.2, its slowformation by cyclisation of the bis-ester, via the ester amide/imidecompound containing one ring, leads to a sustained concentration of theactive cytotoxic species.

What is claimed is:
 1. A compound of formula (II) ##STR8## wherein R₁and R₂ are each separately selected from hydrogen, alkyl, alkenyl andalkynyl groups having up to a maximum of four carbon atoms and beingunsubstituted, and alkyl, alkenyl and alkynyl groups having up to amaximum of three carbon atoms and being substituted by one phenyl,carboxy, alkoxycarbonyl, halogeno (other than fluoro), hydroxy or alkoxygroup, or by one or more fluoro groups, but with the proviso that whenR₁ is hydrogen then R₂ is hydrogen or methyl, or R₁ and R₂ togetherconstitute an ethylene bridging group, and R₃ excludes any group inwhich the bonding carbon atom does not carry at least one hydrogen atom,R₃ being selected from (a) alkyl, alkenyl and alkynyl groups having upto a maximum of ten carbon atoms and being either unsubstituted orsubstituted by one or more alkoxy, carboxy, halogeno, hydroxy,alkoxycarbonyl, benzyloxycarbonyl, cyano, amino, alkylamino,dialkylamino or oxo groups and (b) aralkyl, aralkenyl, and aralkynylgroups in which the aromatic part of the group may optionally besubstituted by one or two substituents selected from halogen, loweralkyl, lower alkoxy, amino and nitro groups or by one methylenedioxygroup, and in which the aliphatic part of the group has up to a maximumof ten carbon atoms and may optionally be substituted by one substituentselected from alkoxycarbonyl and cyano groups, with the further provisothat when each of R₁ and R₂ is hydrogen then R₃ is not methyl and thatthe compound is in the meso or erythro configuration when each of R₁ andR₂ is the same or different unsubstituted or substituted alkyl, alkenylor alkynyl group, and salts thereof with a physiologically acceptableinorganic or organic acid.
 2. A compound according to claim 1, in whichthe aromatic part of the aralkyl, aralkenyl and aralkynyl group R₃ is anunsubstituted or substituted phenyl group.
 3. A compound according toclaim 1, in which the group R₃ excludes any unsubstituted or substitutedalkyl, alkenyl or alkynyl group in which the bonding carbon atom iseither unsaturated or is linked to an atom which is not hydrogen orcarbon.
 4. A compound according to claim 1, in which R₃ is selected fromunsubstituted alkyl, alkenyl and alkynyl groups and substituted alkylgroups as defined under (a) having one or, in the case of alkoxycarbonylgroups, one or two substituents.
 5. A compound according to claim 1, inwhich R₃ is selected from methyl, ethyl, n-propyl, n-butyl, isobutyl,allyl, propargyl, benzyl, α-methylbenzyl, α-ethoxycarbonylbenzyl,nitrobenzyl, aminobenzyl, chlorobenzyl, dichlorobenzyl,chloro-3,4-methylene-dioxybenzyl, methoxybenzyl, dimethoxybenzyl,methylbenzyl, dimethylbenzyl, cinnamyl, methoxyethyl, ethoxyethyl,propoxyethyl, butoxyethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl,ethoxycarbonylmethyl, ethoxycarbonylethyl, ethoxycarbonylpropyl,carboxymethyl, carboxyethyl, carboxypropyl, benzyloxycarbonylmethyl,benzyloxycarbonylethyl, benzyloxycarbonypropyl, t-butoxycarbonylmethyl,t-butoxycarbonylethyl, t-butoxycarbonylpropyl,di-(ethoxycarbonyl)-methyl, cyanomethyl, acetonyl, phenacyl, and3-dimethylaminopropyl, with the proviso that each bonding carbon atom islinked only to atoms which are hydrogen or carbon.
 6. A compoundaccording to claim 5, in which R₃ is selected from substituted benzylgroups as defined therein.
 7. A compound according to claim 1, in whichthe substituted alkyl, alkenyl and alkynyl groups from which R₁ and R₂are selected are substituted by one halogeno (other than fluoro),hydroxy or alkoxy group or by one or more fluoro groups.
 8. A compoundaccording to claim 1, in which R₁ and R₂ are selected from hydrogen andunsubstituted alkyl, alkenyl and alkynyl groups, or R₁ and R₂ togetherrepresent an ethylene bridging group.
 9. A compound according to claim8, in which R₁ and R₂ are each hydrogen, R₁ is methyl and R₂ ishydrogen, methyl, ethyl, n-propyl, isopropyl, allyl or propargyl, R₁ andR₂ are each separately selected from ethyl, n-propyl, isopropyl, allyland propargyl, or R₁ and R₂ together represent an ethylene bridginggroup.
 10. A compound according to claim 1, in which R₁ and R₂ are eachhydrogen, R₁ is methyl and R₂ is hydrogen, methyl or ethyl, or R₁ and R₂are each ethyl, and R₃ is selected from methyl, ethyl, isobutyl, allyl,propargyl, benzyl, α-methylbenzyl, α-carbethoxybenzyl, o-nitrobenzyl,aminobenzyl, 2,6-dichlorobenzyl, methoxyethyl, ethoxyethyl,propoxyethyl, butoxyethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl,ethoxycarbonylmethyl, di-(ethoxycarbonyl)-methyl,benzyloxycarbonylmethyl, ethoxycarbonylpropyl, carboxymethyl andacetonyl, with the proviso that each bonding carbon atom is linked onlyto atoms which are hydrogen or carbon.
 11. A compound according to claim1, in which R₁ and R₂ are each hydrogen.
 12. A compound according toclaim 1, in which R₁ is methyl and R₂ is hydrogen.
 13. A compoundaccording to claim 1, in which the compound is in the form of a saltwith methane sulphonic acid, isethionic acid or tartaric acid.
 14. Acompound according to claim 1, in which R₃ is selected from alkyl,alkenyl, alkynyl and alkoxyalkyl groups having up to a maximum of tencarbon atoms.
 15. A compound according to claim 1, in which R₃ is anaralkyl group in which the aromatic part of the group may optionally besubstituted by one or two substituents selected from halogen, loweralkyl, lower alkoxy, amino and nitro groups or by one methylenedioxygroup, ad in which the alkyl part of the group has a maximum of tencarbon atoms and may be substituted by an alkoxycarbonyl or cyano group.16. A compound according to claim 15, in which the aralkyl group is aphenylalkyl group which may optionally be substituted as described inclaim
 15. 17. A compound according to claim 1, in which R₃ ishalogenoalkyl, hydroxyalkyl, alkoxycarbonylalkyl,di-(alkoxycarbonyl)-alkyl, benzyloxycarbonylalkyl, cyanoalkyl,aminoalkyl or di-(alkylamino)-alkyl group, with the alkyl part in anygroup containing not more than ten carbon atoms.
 18. A compoundaccording to claim 1, in which R₃ is acetonyl or phenacyl.
 19. Acompound according to claim 1, in which R₃ is propargyl. 20.dl-NN'-Dipropargyloxycarbonylmethyl-NN'-diaminocarbonylmethyl-1,2-diaminopropane,and salts thereof with a physiologically acceptable inorganic or organicacid.